<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .a {
            width: 200px;
            height: 400px;
            background-color: #f00;
            float: left;
        }

        .b {
            /* width: 100% - 200px; */
            height: 500px;
            background-color: #ff0;

            /* overflow: hidden; */
            /* margin-left: 200px; */

            position: absolute;
            left: 200px;
            right: 0;
        }
    </style>
</head>

<body>

    <!-- 
        后台管理系统
            两栏式布局：一侧固定，另一侧宽度自适应
            没有版心
     -->

    <div class="a"></div>
    <div class="b"></div>

</body>

</html>